Process for manufacturing foam-filled extruded products

ABSTRACT

A process for fabricating an article having a rigid foam core and a resilient outer plastic shell by extruding heated thermoplastic material to form the shell, partially hardening the extruded a plastic shell, injecting a liquid foam material into the interior of the partially hardened plastic shell, and cooling the shell and the liquid foam material to fully harden the plastic shell and the foam under conditions which cause the article to have a predetermined shape and size.

TECHNICAL FIELD

The present invention is directed to a process for manufacturingfoam-filled plastic extruded products.

BACKGROUND OF THE INVENTION

Traditionally, wood products have been a primary source of materials foruse in construction. However, wood products are becoming increasinglyscarce due to the harvesting of trees at ever faster rates and therather limited rate at which timber resources can be replenished. Also,environmental concerns and environmental regulations directed toconservation or preservation of forests tend to restrict theavailability of wood products. With diminishing availability of timberresources, wood products are becoming increasingly expensive. There is,therefore, a substantial need for long-lasting substitute constructionmaterials that can lessen the need to harvest timber resources.

One approach to addressing the above need is to provide a substitutereplacement product made of plastic, rather than wood. However, thereplacement or substitute product needs to be stable, rigid, andrelatively inexpensive. It also needs to be easily fabricated and usedin the field.

U.S. Pat. No. 5,253,458 describes a simulated log made from a castpolyvinylchloride (PVC) pipe, selectively filled with a hard cast foamor a bead type foam. Said patent further describes that the cast PVCpipe is first manufactured and then subsequently filled with the foamfiller. This type of manufacturing tends to require excessive numbers ofmanufacturing operations, and at substantial cost.

Accordingly, it can be seen that there is yet a need in the art for aprocess of manufacturing foam-filled extruded plastic products, such asa replacement for traditional wood products, wherein the process shouldprovide a strong finished product at minimal cost and with a minimalnumber of manufacturing steps. It is to the provision of such a processthat the present invention is primarily directed.

SUMMARY OF THE INVENTION

Briefly described, in a preferred form the present invention comprises aprocess for fabricating an article comprised of an inner rigid foam coreand an outer resilient plastic shell, with the article having apredetermined size and shape. The method comprises the steps ofextruding a thermoplastic material and, during the extrusion, injectinga liquid foam material into the interior of the extruded thermoplasticmaterial so that the extruded plastic shell and the expanded liquid foamcore are made together at the same time, thereby minimizing the numberof manufacturing steps and the attendant cost. This also tends topromote a very strong bond between the foam core and the extrudedplastic shell, thereby increasing the structural rigidity of theresulting foam-filled extruded plastic product. This integrated processfor manufacturing the foam-filled extruded product also tends tominimize the cost of manufacturing the product.

In another preferred form the invention comprises a process forfabricating an article comprised of an inner rigid foam core and anouter resilient plastic shell, with the article having a predeterminedsize and shape. The process includes the steps of extruding athermoplastic material, initially hardening the thermoplastic materialto a certain extent, injecting a liquid foam material into the initiallyhardened plastic material, further hardening the plastic material toobtain the predetermined size and shape, and cutting the article to adesired length.

Accordingly, it is a primary object of the present invention to providea process for manufacturing a foam-filled extruded product which iseconomical in application, reliable, and simple.

It is another object of the present invention to provide a process formanufacturing a foam-filled extruded product which results in evendistribution of the foam within the interior of the extruded product.

It is another object of the present invention to provide a process formanufacturing a foam-filled extruded product which results in a strongbond between the extruded shell and the foam core.

These and other objects, advantages, and features of the invention willbecome more apparent upon reading the following specifications inconjunction with the accompanying drawing figure.

BRIEF DESCRIPTION OF THE DRAWING FIGURE

FIG. 1 is a schematic diagram of a system for carrying out the processfor manufacturing a foam-filled extruded product according to apreferred form of the invention and showing various mechanical andelectrical components for use therein in schematic form.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now in detail to the drawing figure, in which like referencenumerals represent like parts, FIG. 1 shows a manufacturing system 10for carrying out the process according to the invention. Manufacturingsystem 10 includes first and second extrusion lines 11 and 12, with two(2) lines shown for illustration purposes. Of course, those skilled inthe art will readily recognize that only one extrusion line could beemployed or that more than two extrusion lines could be employed, asdesired. The extrusion lines 11 and 12 are each controlled by a commonelectronic controller 13. The electronic controller can take any ofseveral known forms, such as a programmable logic controller (PLC) or apersonal computer adapted for such application.

A common extruder 14 feeds both extrusion lines 11 and 12. The extrudercan be of any number of known types, but typically includes an internalauger (not shown) for metering and pumping plastic pellets or powdersand a heating element for heating the plastic pellets or powders to meltthem to provide a heated thermoplastic discharge suitable for use in theextrusion lines. Moreover, as those skilled in the art will alsounderstand, the extruder 14 typically is fed by known metering orblending equipment for providing a desired controlled quantity ofplastic pellets to the extruder and/or for maintaining a preset recipeof plastic pellets or powder to provide a desired composition of theplastic to be extruded. The extruder output is heated thermoplasticwhich is forced through a "Y-block" or divider 16 for providing equalflows of plastic to first and second crosshead dies 17 and 18. Thesecrosshead dies 17 and 18 are somewhat similar in construction andoperation to those used to coat electric wire with an outer plasticinsulation sheath. Each of the crosshead dies 17 and 18 includes aninternal (unshown) mandrel or core element, which together with theouter (interior) surface of the crosshead die operate to define theshape and wall thickness of the extruded plastic product discharged fromthe crosshead dies.

Initial sizing and cooling sleeves 21 and 22 are positioned to receivethe extruded product from the crosshead dies 17 and 18. These initialsizing and cooling sleeves 21 and 22 are conventional vacuum units.These initial sizing and cooling sleeves provide a rough initial shapeand some initial cooling to stabilize the extruded plastic shell. Theextruded plastic shell is indicated at S1 and S1' in FIG. 1. As depictedin the figure, the initial sizing and cooling sleeves 21 and 22 arespaced a short distance from the crosshead dies 17 and 18 to expose thissection of the outer shell S1 and S1'. This then allows sensors to bepositioned adjacent the outer shells S1 and S1' to detect anyinterruption in the extrusion of the outer shells. Such sensors aredepicted at 23 and 24 in FIG. 1 and can take any number of known forms.For example, a photo emitter and a photo detector can be used to detectwhen there is a break in the extrusion. Alternatively, a motion sensoror proximity sensor can be used.

Another pair of similar sensors 25 and 26 are positioned downstream(after) the initial sizing and cooling sleeves 21 and 22. These secondsensors 25 and 26 also operate to detect a break in the outer shell ofthe extrusion.

A pair of foam mixing and metering devices 31 and 32 pump meteredquantities of liquid foam at controllable pressures through liquid foamsupply conduits 33 and 34, preferably at room temperature. These liquidfoam supply conduits 33 and 34 extend through the crosshead dies 17 and18 and through the initial sizing and cooling sleeves 21 and 22. Theopen (discharge) ends 35 and 36 are positioned downstream of the initialsizing and cooling sleeves 21 and 22. Thus, the liquid foam is pumpedand metered from the foam mixing and metering devices 31 and 32 throughthe crosshead dies 17 and 18 and through the initial cooling and sizingsleeves 21 and 22 and into the interior of the initially cooled andsized outer shells S2 and S2'.

Secondary sizing and cooling sleeves or tanks 37 and 38 are positioneddownstream from the open discharge ends 35 and 36 of the liquid foamsupply conduits 33 and 34. The open ends of liquid foam supply conduits33 and 34 are positioned approximately 6" to 12" from the secondarysizing and cooling tanks 37 and 38 so that the liquid foam is allowed todrop away from the extrusion lines in the event that a break occurs. Inthis way, the secondary sizing and cooling sleeves 37 and 38 receive theextruded outer shells S2 and S2' (which have been initially cooled andsized), now filled with expanding or expanded foam. The secondary sizingand cooling tanks provide the foaming and cross-linking reactions andcool the overall article, thereby causing the foam to solidify and thearticle to take the desired shape. These secondary sizing and coolingsleeves or tanks 37 and 38 further define the exterior dimensions andshape of the outer shell S2 and S2', with the discharge from thesesleeves or tanks being a finished extruded product P and P'. Thesecondary sizing and cooling sleeves or tanks 37 and 38 are rather longin comparison to the initial sizing and cooling sleeves 21 and 22 andutilize a water jacket or water film to minimize the friction betweenthe shell S2 and S2' and the secondary sizing and cooling sleeves 37 and38. The water film or jacket also helps to cool the outer shells S2 andS2' (and the liquid foam contained therein, now rapidly cooling andhardening to form a rigid structure). The water is preferably at atemperature of approximately 60° F. and the foam expands and sets within30 to 45 seconds. The water also helps tend to avoid marring theexternal finish of the outer shells of the product P and P'.Furthermore, the secondary sizing and cooling sleeves are preferablycoated with chrome or Teflon® to further reduce friction. The initialsizing and cooling sleeves 21 and 22 may also be coated with chrome orTeflon® if desired. The use of water jacketed sizing and cooling sleevesis known in the art in connection with very large diameter extrusions,such as 36-inch diameter plastic pipe. However, the use of such awater-jacketed sleeve in connection with small diameter extrusions (onthe order of 12 inches or less) has not been known by the applicantsheretofore. Nor have the applicants been aware of the use of both aninitial sizing and cooling sleeve (21 and 22) together with a secondarysizing and cooling sleeve (37 and 38).

Pullers 41 and 42 operate to pull the extruded product P and P' alongthe extrusion lines 11 and 12. These pullers are of conventional designand include, for example, endless tracks which engage the outer surfaceof the extruded product for pulling the extruded product in a downstreamdirection (indicated by arrow D). Each of these pullers has associatedtherewith a torque sensor 43, 44 for monitoring the torque of the pullerbeing applied to the product P and P'. If the torque exerted by thepullers 41 or 42 suddenly drops to zero or near zero, this is anindication that a break has occurred in the extrusion.

The product P and P' is further conveyed by the pullers 41 and 42 to asaw or other cut off device 45, 46 for cutting the extruded product P,P' into pieces of a predetermined or desired length.

Electrical cabling 51-58 connects the controller 13 with the foam mixingand metering devices 31 and 32 and with the sensors 23 and 24, 25 and26, and 43 and 44.

In operation, liquid foam is pumped from the liquid foam mixing andmetering devices 31 and 32 through the conduits 33 and 34 through thecrosshead dies 17 and 18 and ultimately discharges at the discharge ends35 and 36 into the interior of the semi-cooled outer shells S2 and S2'.This takes place at the same time as the extrusion of the outer shellsby the crosshead dies 17 and 18, the initial sizing and cooling sleeves21 and 22, and the secondary sizing and cooling sleeves 37 and 38. Thissimultaneous injection of the liquid foam into the interior of theextruded shell during the extrusion process provides for superiorbonding of the foam to the interior wall of the outer shell. This alsoprovides for superior filling (avoiding voids) of the foam in theinterior of the outer shell. Another advantage of this simultaneousinjection of the liquid foam is that it minimizes the number ofmanufacturing steps or subsequent steps that have to be taken. This alsotends to make the manufacture of the foam-filled extruded product veryeconomical and requires a minimal amount of manufacturing floor space.The result is an economical, extremely strong final product.

The liquid foam is preferably polyurethane, but other materials such aspolyesters and epoxies can be used as well. The outer polymer shell ispreferably made from polyvinylchloride, but other materials such asacrylic, ABS, polyethylene, polypropylene, polycarbonate, and blends andalloys of two or more of these materials can be used. The polymer shell,once hardened, will preferably have a thickness ranging from 0.005 to0.250 inches and the foam will preferably have a density ranging from 1to 30 lbs/ft³.

While the invention has been disclosed in preferred forms, it will beapparent to those skilled in the art that many additions, deletions, andmodifications may be made therein without departing within the spiritand scope of the invention as set forth in the following claims:

What we claim is:
 1. A process for fabricating an article having aninner rigid foam core and an outer resilient plastic shell, said articlehaving a predetermined length and shape, said method comprising thesteps of:(a) extruding a thermoplastic material around a tube having aliquid foam material flowing therethrough; (b) partially hardening thethermoplastic material while it is around the tube to form the outerresilient plastic shell; (c) transporting the plastic shell over anopening formed in the tube and injecting liquid foam material into theplastic shell; (d) transporting the plastic shell filled with the liquidfoam material through a cooling and sizing tank whereby the liquid foammaterial is hardened to form the inner rigid foam core and the articlecomprising the inner rigid foam core and the outer resilient plasticshell is shaped into the predetermined shape; (e) transporting thearticle out of the cooling and sizing tank; and (f) cutting the articleto a predetermined length.
 2. The process of claim 1 wherein thethermoplastic material is PVC.
 3. The process of claim 1 wherein theliquid foam material is urethane.
 4. The process of claim 1 wherein themethod is a continuous method.
 5. The process of claim 1 furthercomprising monitoring the shell to detect an absence of the shelladjacent the opening formed in the tube and halting the flow of theliquid foam material into the tube when the shell is absent adjacent theopening.
 6. The process of claim 1 wherein the liquid foam material ispolyester.
 7. The process of claim 1 wherein the liquid foam material isepoxy.